This section describes background subject matter related to the disclosed embodiments of the present invention. There is no intention, either express or implied, that the background art discussed in this section legally constitutes prior art.
A glaze is a specialized form of glass and therefore can be described as an amorphous solid. Glazing is the process of coating the part with a layer of glaze. A glass ceramic is a specialized form of ceramics, which is formed first as a glass and then made to crystallize partly through a designed heat treatment which involves controlled cooling.
Unlike traditional sintered ceramics, glass ceramics do not have pores between crystal grains. The spacing between grains is filled with the glass. Glass ceramics share many properties with both glass and traditional crystalline ceramics. After adjusting the composition of glass ceramics by processing technique, the final material may exhibit a number of advanced properties that the traditional ceramics do not have.
Glazes and glass ceramics have long been used to provide protective coatings. To form the protective coatings, typically a powder of an oxide, which may be in combination with a non-oxide, is placed into a suspending medium, to which a binder composition may be added, this combination of ingredients produces a slurry which is applied over a substrate which is to be coated, and then the slurry is sintered under controlled time, temperature and environmental conditions. During sintering, when the fluid coating material is cooled rapidly, typically a glaze is produced; when the coating material is cooled slowly, a glass-ceramic is obtained.
The physical properties of the coating obtained, such as thermal conductivity, thermal expansion coefficient, hardness, and toughness, for example, can be adjusted by changing the composition of the ceramic powder, and/or the processing technique. The thickness of the coating, for a given application process, may be “fine tuned” by adjusting the slurry viscosity, pH, and binder, for example. Depending on the composition of the coating and the substrate, and the application process, a transition layer may be formed between the substrate and portion of the coating which is in contact with the substrate. A transition layer formed in-situ during application of the coating to the substrate surface may provide better chemical bonding between the substrate and the coating and may also dissipate the stress due to thermal expansion difference between the substrate and the coating.
To apply a coating, a slurry containing the ceramic powder, suspension medium, binder and possibly dopants of various kinds is typically applied over the surface of a substrate using a technique known in the art, such as painting, dipping, spraying, screen printing, or spin-on, by way of example. The substrate must be able to withstand the sintering temperature required to form the coating. The coating is then sintered at a sufficient temperature and for a period of time to permit the coating to form. The coating performance in a given application is limited by the composition of the coating and the processing conditions used to apply the coating.
Processing chamber liners and component apparatus present within processing chambers which are used in the fabrication of electronic devices and micro-electro-mechanical structures (MEMS), for example and not by way of limitation, are frequently constructed from ceramics such as aluminum oxide and aluminum nitride. While the plasma erosion resistance for these materials in a fluorine containing plasma of the kind typically used for etching silicon-containing electronic device structures is better than a number of materials which were used in the processing art even 5 years ago, there is constantly an effort to try to improve the erosion resistance of etch processing components, as a means of extending the lifetime of the processing apparatus and of reducing metal contamination and particle formation during device processing. Not only is the processing apparatus very expensive, the production down time caused by the need to replace apparatus which is not functioning well due to erosion is also very expensive.
Solid yttrium oxide component structures have demonstrated considerable advantages when used as semiconductor apparatus components in reactive plasma processing. A yttrium oxide solid component substrate typically comprises at least 99.9% by volume yttrium oxide, has a density of at least 4.92 g/cm3, and a water absorbency of about 0.02% or less. The average crystalline grain size of the yttrium oxide is within a range of about 10 μm to about 25 μm. The co-inventors of the present invention developed a yttrium oxide-containing substrate which includes impurities which are equal to or less than the following maximum concentrations: 90 ppm Al; 10 ppm Ca; 5 ppm Cr; 5 ppm Cu; 10 ppm Fe; 5 ppm K; 5 ppm Mg; 5 ppm Na; 5 ppm Ni; 120 ppm Si; and 5 ppm Ti. This yttrium oxide-comprising substrate provided improvements over substrates previously known in the art. A yttrium oxide-comprising substrate of this general composition which included up to about 10% by volume of aluminum oxide was also developed.
In a reactive plasma etch rate test, where the reactive etchant plasma contains plasma species generated from a plasma source gas of CF4 and CHF3, a solid Yttrium oxide substrate component resists etch by the plasma better than solid aluminum oxide substrate or solid aluminum nitride substrate, but not as well as the components of the present invention either in solid form or as coatings over underlying substrates.